We have proposed a model for metabolic regulation of lipoprotein lipase (LPL) in adipose tissue. The enzyme is synthesized in the adipocyte and released or secreted from the cell in an activated form. LPL is then transported to the lumen surface of the capillary endothelium where chylomicron and VLDL substrates are sequestered and hydrolysis takes place. The studies proposed will allow us to further elaborate this model of LPL regulation. Specifically, studies of the LPL releasing factor of serum and other possible releasing agents should make clear some of the metabolic events which govern the egress of LPL from adipocytes. Use of the antibody to LPL will indicate whether variability in intra- and extracellular LPL activity results from synthesis of new enzyme protein or activation processes. We propose to test whether endothelial cells synthesize LPL themselves or only provide binding sites for the enzyme synthesized in and released from adipocytes. If endothelial cells bind LPL, what is the nature and extent of this binding and what factors control it? The proposed biochemical studies on the composition of LPL will allow us to compare LPL from various tissues and hopefully to extend our detailed model for regulation of adipose LPL to that of heart.